This invention relates to a rotatable tool intended for chip removing or chip forming machining, comprising two portions, viz. a rotatable holder part mountable in a machine, and a cutting part that is detachably connected to a front end of the holder part, a forwardly open slot being formed in a front end portion of the holder part, which slot separates two or more elastically flexible or resilient branches.
Chip forming tools of the type that uses a holder part or basic body as well as a separate, replaceable cutting part may in practice be of highly varying shapes and may consist of, for instance, drilling tools, milling tools, such as shank-type cutters and slot cutters, respectively, thread cutters, etc. The holder part usually consists of a long narrow, cylindrical shank. In modern machine tools, the holder parts are so sophisticated and expensive that they, for economical reasons, cannot be integrated with the cutting part, which constitutes the wearing part of the tool. In other words, it is profitable to make the proper cutting part as a separate, detachable unit (usually denominated xe2x80x9cloose topxe2x80x9d by those skilled in the art), which may be replaced after wear-out, while the expensive holder part may be used for a longer period of time.
Previously known cutting tools of the type in question may be divided into two main categories, a first of which being based upon the idea of attaching the cutting part at the front end of the holder part by means of a short screw, which extends through a through hole in the cutting part and is tightened in a female thread that extends axially in the holder part and is open at the front end thereof. Examples of such tools are disclosed in U.S. Pat. No. 5,607,263, DE-34 48 086-C2 and DE-297 23 558-U1. A disadvantage of said kind of tool is, however, that cutting edges cannot be formed in the central area of the front end of the cutting part. The consequence of this is that the cutting part can only be made for certain types of milling (e.g., milling of T-slots), but not for drilling and other milling operations.
Another category of tools use a drawbar that is disposed within an axial bore within the holder part and includes means at the front end there of for clamping the cutting part. Tools having drawbars for the cutting parts are previously known from, for instance, EP 0 911 10 (corresponding U.S. Pat. No. 6,053,670), WO 96/34714 (corresponding U.S. Pat. No. 5,947,660 and U.S. Pat. No. 6,183,688) and WO 01/30524. A disadvantage of said type of tools is, however, that tightening of the drawbar takes place in the area of the rear end of the drawbar and the holder part. This means that the holder part has to be removed from the machine in question to exchange the cutting part.
In U.S. Pat. No. 5,904,455, a drilling tool is disclosed, the holder part or shank of which in the front end thereof possess a recess defined by two branches for receipt of a cutting part. Furthermore, in the front end portion of the holder part, a narrow slot is formed with the purpose of enabling elastic deflection of the branches. The two branches are formed having inwardly turned flank surfaces, which may be resiliently pressed against contact surfaces on the sides of the cutting part, more precisely thanks to wedge surfaces being pressed into a V slot in the rear end of the cutting part. The wedging is guaranteed by means of an axial screw within the holder part. A disadvantage of said tool is, however, that the cutting part as well as the holder part has to be manufactured with a very high dimensional accuracy. Another disadvantage is that the tool demands dismounting from the appurtenant machine in order to enable manipulation of the screw in connection with exchange of the cutting part.
The present invention aims at obviating the above-mentioned disadvantages of previously known cutting tools of the type in question and at providing an improved cutting tool. Thus, a primary object of the invention is to provide a cutting tool that not only allows simple mounting and dismounting of the cutting unit without requiring that the holder part be removed from a machine, but also enables cutting edges or cutting inserts to be disposed at the center of the front surface of the cutting part. An additional object is to provide a tool, the two main parts of which, i.e., the cutting part and the holder part, respectively, can be series produced separately in a simple and cost-effective way while guaranteeing a good centering of the cutting part in relation to the holder part. Among other things, each one of the two parts should be able to be produced by means of simple machining operations and with a minimum of advanced grinding operations. Yet an object of the invention is to provide a tool that minimizes the wear of the holder part, thereby securing a long service life of the same.
According to the invention, at least the primary object is attained by a rotatable tool for chip removing machining which comprises a holder part and a cutting part. The holder part defines a center axis of rotation and includes an axially front end in which a slot is formed between elastically flexible branches of the holder part. The branches are elastically deformable or deflectable from a rest state thereof. The cutting part is detachably connected to the branches. The holder part and the cutting part form a male/female coupling comprising a male part disposed on either the holder part or the cutting part, and a female part formed in the other of the holder part and the cutting part. The male part is received in the female part. A cross-section of each of the male part and the female part is at least partly circular. The one of the male part and the female part disposed on the holder part has a diameter variable in size in response to manually induced elastic deformation of the branches out of their rest state, wherein the elastic deformation causes a smallest diameter of the female part to be larger than a largest diameter of the male part to permit joining of the male part and the female part, and wherein a return of the branches to their rest state causes a minimum diameter of the female part to be smaller than a largest diameter of the male part to prevent removal of the cutting part from the holder part.